1. Field of the Invention
This invention is related to a flyback transformer for developing a high voltage which is applied to an anode of a cathode ray tube. More particularly, the present invention is related to a circuit for detecting a wrong operation of a flyback transformer.
2. Description of the Prior Art
Generally a high voltage, which is applied to an anode of a cathode ray tube of a display apparatus such as a television, a monitor, etc., is developed by a flyback transformer(hereinafter, referred to as FBT). A high voltage generating circuit develops a low voltage pulse according to a horizontal driving signal which is provided from a horizontal driving circuit, and provides the low voltage pulse to a low-voltage coil of the FBT in order to make it possible to generate the high voltage. The high voltage generating circuit rectifies an induced voltage pulse which is outputted from a high-voltage coil of the FBT to generate the high voltage, and provides the high voltage to the anode of the cathode ray tube(hereinafter, referred to as CRT).
One example of a high voltage generating circuit is disclosed in U.S. Pat. No. 5,278,746 issued to Tadahiko Matsumoto on the date of Jan. 11, 1994. The high voltage generating circuit suggested by Tadahiko Matsumoto includes a FBT having a low-voltage coil and a high-voltage coil and a first switching element disposed in a current path among a drive power source, the low-voltage coil and ground. The first switching element is turned on and off to charge and discharge a resonance capacitor, thereby generating flyback pulse. The high voltage generating circuit also detects an output voltage of the high-voltage coil, and controls a peak value of a flyback pulse, which is applied to the low-voltage coil on the basis of the detected output voltage. The high voltage generating circuit further includes a second switching element disposed in the current path among the drive power source, the low-voltage coil and ground. The second switching element is turned on the moment that the first switching element is turned off, thereby transferring electrical energy stored in the low-voltage coil to the resonance capacitor. After the transfer of the electric energy, a charging capacitor is charged by an inverse current flowing from the resonance capacitor to the drive power source. Therefore, the high voltage generating circuit suggested by Tadahiko Matsumoto can control a high voltage which is generated from the high-voltage coil of the FBT.
However, though Tadahiko Matsumoto's high voltage generating circuit can regulate the output voltage of the FBT, the circuit has a problem that when the FBT is out of order, the circuit causes the FBT to develop a dangerously high voltage.